Electrode activation and passivation of solid oxide fuel cell electrodes

The performance of anode-supported cells with a composite LSM-YSZ cathode and an LSM current collector was investigated. Over the first 48 hours, after the application of a constant current, the cell voltage was observed to increase by up to 20%. When the current was switched off, the cell resistance increased significantly over the next four days at open circuit conditions. Apparently, at OCV conditions cell passivation occurs. The cell gradually reactivates, once the current is switched on again. Part of this activation/passivation process is fast enough to influence the resistance of the cell during i-V measurements (over less than 1 hour) and a considerable hysteresis is observed in the cell voltage during these measurements.

Impedance spectroscopy was used to investigate the activation/passivation process. It was found that the series resistance and the part of the polarisation impedance above approximately 100 Hz were not influenced by the activation/passivation process. The part of the polarisation impedance between I and 100 Hz was highly influenced by the activation/passivation process and during cell polarisation this part of the polarisation impedance was up to 40% lower than at open circuit conditions. This frequency range of the spectrum was also sensitive to the oxygen partial pressure at the cathode side, indicating that it is the cathode that activates and passivates.